1. Field of the Invention
The present invention relates to data compression/decompression techniques for data transmitted in a telecommunication system, and in particular, to data compression/decompression techniques for data transmitted in a paging system.
2. Description of the Related Art
Paging systems can now send alphanumeric messages to subscribers virtually anywhere in the world. To page a subscriber, a caller need not know the subscriber's location. The caller simply calls a paging system control terminal and provides the personal identification number (PIN) of the subscriber and an alphanumeric message, typically including the caller's telephone number and/or a brief message. The paging system control terminal transmits the message to one or more geographic regions.
Conventional data transmission techniques used in conventional paging systems require that each message be transmitted in accordance with a predetermined protocol. One example of such a protocol is the Telocator Network Paging Protocol (TNPP), which is an open data communication protocol used to transfer paging information from a paging system control terminal to a transmitting device.
FIG. 1 illustrates the TNPP protocol 100 in block format. The TNPP protocol 100 includes start of header flag 102, header section 104, header extension section 106, start of text flag 108, data block or blocks 110, end flag 112, and block check code section 114. These flags and sections format the necessary header and identification information and provide for the page message in the data block or blocks 110. The present invention relates to the compression of data for data block of block 110. At a paging transmitter, the TNPP protocol is reconfigured into a paging protocol for transmission to one or more page receivers.
Traditionally, page messages are transmitted using either an ASCII transmission format or a preestablished phrase technique. An example of a page message to be transmitted is: "Please call Mr. Jones at 501-555-1234 regarding invoice number 56789." FIG. 2 illustrates an ASCII transmission format necessary to transmit this exemplary message. Each character, punctuation mark, and space (sp) of this message requires eight (8)-bits of binary information to be transmitted. As a result, even this simple message comprises a significant string of binary data (specifically 544 bits), which increases the operating costs of the corresponding paging system. This increased cost is ultimately borne by the subscriber to the paging service.
One conventional technique for reducing the amount of information to be transmitted for a page message is the preestablished phrase technique, wherein predetermined codes are assigned to preestablished phrases to reduce the amount of data to be transmitted. For example, the phrase "Please call the office" may be associated with a sixteen (16)-bit code which is transmitted to the page receiver. Although this technique has the advantage of reducing data to be transmitted for some messages, it is inherently limited in that only preestablished phrases can be codified and transmitted. If the message to be transmitted is not a preestablished phrase, then the complete ASCII representation of the message must be transmitted. Thus, while the preestablished phrase technique has some advantages, it is inherently limited and inflexible and does not provide an accommodating solution to the problem of data transmission for unique page messages.